The present invention relates to black iron-based particles, and a black paint and a rubber or resin composition using the black iron-based particles, and more particularly, to black iron-based particles which are excellent in dispersibility, blackness, tinting strength and acid resistance and exhibit a less magnetization value, and a black paint and a rubber or resin composition using such black iron-based particles.
As typical black pigments, there are known magnetite particles, carbon black, graphite fluoride or the like. These black pigments have been generally used as colorants for paints, printing inks, cosmetics, rubber and resin compositions or the like for a long time.
In recent years, from the standpoints of good safety and hygiene, high working efficiency capable of meeting current energy saving requirements, and enhancement in various properties, it has been strongly required to provide black pigment particles having a good workability and various excellent properties which are safe and harmless, and excellent in not only blackness and tinting strength but also dispersibility.
However, the magnetite particles tend to be re-agglomerated together due to high magnetic properties thereof despite safety and harmlessness, resulting in difficult dispersion and poor workability.
Also, the carbon black is in the form of ultrafine and bulky particles having a particle diameter of about 0.01 to 0.1 μm, and therefore, tends to be deteriorated in handling property and workability. Further, it has been reported that the carbon black has problems concerning safety and hygiene, such as carcinogenesis.
The graphite fluoride is not a safe and harmless substance, and tends to exhibit an insufficient dispersibility.
On the other hand, there have been proposed Mn-containing hematite particles which are safe and harmless, and usable as a non-magnetic black pigment (Japanese Patent Application Laid-open (KOKAI) No. 10-279314 (1998)). However, it has been recently reported that the Mn-containing compounds have problems concerning safety, such as adverse influences on human lung and nervous system.
Therefore, at present, it has been strongly required to provide a black pigment which is hardly magnetically agglomerated together, has good safety and harmlessness, and exhibits an excellent blackness.
In order to improve the workability, the pigment is required to have a non-magnetic property, an appropriate particle size, an excellent dispersibility and a good handling property.
The good dispersibility of the pigment contributes to not only enhancement in clearness of color tone and basic properties inherent to the pigment such as tinting strength and hiding power, but also enhancement in gloss and clarity of the resultant coating film as well as film properties thereof such as acid resistance.
On the other hand, in recent years, natural and life environmental problems such as acid rain have been become more worse. In particular, film-forming materials and rubber or resin compositions used outdoors have been more strongly required to exhibit a high acid resistance.
Conventionally, there are known the black pigment composed of a mixture of Fe2TiO5 and a Fe2O3—FeTiO3 solid solution (Japanese Patent Application Laid-open (KOKAI) No. 3-2276 (1991)); the black pigment having a particle structure in which a rutile-type TiO2 phase as a base substance is coated with a Fe2TiO4 phase (Japanese Patent Application Laid-open (KOKAI) No. 2002-129063); the black iron-based particles composed of a mixture of a Fe2O3—FeTiO3 solid solution or a Fe2O3—FeTiO3 solid solution, and an iron-based oxide having a spinel type structure (Japanese Patent Application Laid-open (KOKAI) No. 2004-161608); or the like.
Thus, at present, it has been most strongly required to provide a black pigment which is not only excellent in dispersibility, acid resistance, tinting strength and blackness, but also exhibits a less magnetization value. However, the black pigment having such properties has not been obtained until now.
This is, although the non-magnetic particles described in Japanese Patent Application Laid-open (KOKAI) No. 3-2276 (1991) are iron and titanium composite oxide particles, the ratio between contents of iron and titanium in the vicinity of the surface of the respective particles is not taken into consideration. As a result, the obtained particles may fail to satisfy the dispersibility, acid resistance, blackness and tinting strength as required.
The black composite oxide described in Japanese Patent Application Laid-open (KOKAI) No. 2002-129063 which has a particle structure in which a rutile-type TiO2 phase as a base substance is coated with a Fe2TiO4 phase, may also fail to fully satisfy the dispersibility, acid resistance, blackness and tinting strength as required.
Although the black iron-based particles described in Japanese Patent Application Laid-open (KOKAI) No. 2004-161608 are iron and titanium composite oxide particles, the ratio between contents of iron and titanium in the vicinity of the surface of the respective particles is not taken into consideration. As a result, the obtained particles may fail to satisfy the dispersibility, acid resistance, blackness and tinting strength as required.
As a result of the present inventors' earnest study for solving the above problems, it has been found that by controlling a titanium element content (A) in iron/titanium composite oxide particles constituting the black iron-based particles to 5 to 35% by atom based on an iron element content and controlling a ratio of a titanium element content (B) (based on an iron element content contained in the portion dissolved) in a portion of the iron/titanium composite oxide particles constituting the black iron-based particles, which is dissolved therefrom until reaching an iron element dissolution percentage of 1% by weight to the above titanium element content (A), to not less than 1.0, the resultant black iron-based particles are surprisingly not only excellent in dispersibility, acid resistance, blackness and tinting strength, but also exhibit a less magnetization value. The present invention has been attained based on the above finding.